Abstract: A nonlinear optical crystal of barium cesium borate, a preparation method and use thereof are provided. The nonlinear optical crystal has a chemical formula of CsBa3B11O20 and a molecular weight of 983.84. The nonlinear optical crystal belongs to an orthorhombic crystal system; a space group of the nonlinear optical crystal is Cmc21; lattice parameters of the nonlinear optical crystal are a=19.011(7) ?, b=10.837(4) ?, c=8.578(3) ?, Z=4, V=1767.4(11) ?3; and a Mohs hardness of the nonlinear optical crystal is 4-5. The nonlinear optical crystal is grown by a flux method. The nonlinear optical crystal of the barium cesium borate obtained is used for a manufacture of non-linear optical devices. The nonlinear optical crystal has a large size of centimeter-scale at least and is prepared by fast, simple and low-cost operations. The nonlinear optical crystal prepared has a large size, a wide light transmission band and good mechanical properties.